Figure 4-7.Diagram of a superheater.one type of boiler to another and from one boilermanufacturer to another. Figure 4-6 shows thearrangement of the steam drum internal fittingsin a single-furnace boiler.. The feedwater pipe receives feedwaterfrom the economizer and distributes it throughoutthe length of the steam drum.. The chemical feed pipe is used to injectchemicals into the boiler to maintain the properpH and phosphate balance in the boiler water.l The surface blow pipe is used to removesuspended solid matter that floats on top of thewater and to lower the steam drum water level,when necessary. The surface blow pipe is also usedto blow water out to lower the chemical level inthe boiler when it becomes too high.. The dry pipe is used to direct the steam tothe steam drum outlet nozzle after it leaves thescrubbers.. The vortex eliminators are used to reducethe swirling motion of the water as it enters thedowncomers.l The baffle plates are used to direct thesteam to the steam separators.l The cyclone steam separators removemoisture from the steam. This is accomplished bythe steam spinning or changing direction. Thewater drains back into the steam drum while thesteam continues upward through a screen andscrubber that removes still more moisture.After the steam leaves the scrubbers, it goesto the dry pipe (fig. 4-6). From there it leaves thesteam drum through the steam drum outlet.Figure 4-7, view A, shows the steam going to theinlet header of the superheater and passingthrough the U-shaped tubes of the superheater tothe next header (fig. 4-7, view B). This header iscalled the first pass or intermediate header. Steammay pass through the U-shaped tubes severaltimes before passing to the outlet header. Eachtime the steam goes from one header to the nextheader it is called a pass. The number of passesthe steam makes in a superheater varies withdifferent boilers and the degree of superheat thatis required for a particular ship.4-9